Straight Dope on Medicine: Curing Atrial Fibrillation

Author

Scott Ganser
October 09, 2023

What is Atrial Fibrillation?

Atrial fibrillation (Afib) is an irregular heart rhythm that begins in your heart’s upper chambers (atria). Symptoms include fatigue, heart palpitations, trouble breathing and dizziness. Afib is one of the most common arrhythmias. Risk factors include high blood pressure, coronary artery disease and having obesity. Untreated Afib can lead to a stroke.[i]

There are three main types of atrial Fibrillation.

· Paroxysmal Afib lasts less than one week and usually stops on its own without treatment.

· Persistent Afib lasts more than one week and needs treatment.

· Long-standing persistent Afib lasts more than a year and is sometimes difficult to treat.

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia worldwide; confers an increased risk of stroke, heart failure, cognitive decline and death, and is associated with quantifiable impairment in quality of life.[ii]

How is atrial fibrillation diagnosed?

· Listening to your heart rhythm with a stethoscope.

· Checking your pulse and blood pressure

· Checking the size of your thyroid gland to identify thyroid problems.

· Looking for swelling in your feet or legs to identify heart failure.

· Listening to your lungs to detect heart failure or infection.

Understanding the Heart's Electrical System

The heart has an internal electrical system that controls the speed and rhythm of the heartbeat. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As it travels, the signal causes the heart to contract and pump blood. The process repeats with each new heartbeat.

Each electrical signal begins in a group of cells called the sinus node, or sinoatrial (SA) node. The SA node is located in the right atrium, which is the heart's upper right chamber. In a healthy adult heart at rest, the SA node fires off an electrical signal to begin a new heartbeat 60 to 100 times a minute. (This rate may be slower in very fit athletes.)[iii]

From the SA node, the electrical signal travels through special pathways to the right and left atria. This causes the atria to contract and pump blood into the heart's two lower chambers, the ventricles. The electrical signal then moves down to a group of cells called the atrioventricular (AV) node, located between the atria and the ventricles. Here, the signal slows down just a little, allowing the ventricles time to finish filling with blood.

Understanding the Electrical Problem in Atrial Fibrillation

In AF, the heart's electrical signal begins in a different part of the atria or the nearby pulmonary veins and is conducted abnormally. The signal doesn't travel through normal pathways, but may spread throughout the atria in a rapid, disorganized way. This can cause the atria to beat more than 300 times a minute in a chaotic fashion. The atria's rapid, irregular, and uncoordinated beating is called fibrillation.

The abnormal signal from the SA node floods the AV node with electrical impulses. As a result, the ventricles also begin to beat very fast. However, the AV node can't conduct the signals to the ventricles as fast as they arrive, so even though the ventricles may be beating faster than normal, they aren't beating as fast as the atria. The atria and ventricles no longer beat in a coordinated fashion, creating a fast and irregular heart rhythm. In AF, the ventricles may beat up to 100-175 times a minute, in contrast to the normal rate of 60-100 beats a minute.

Outlook

People who have AF can live normal, active lives. For some people, treatment can cure AF and return their heartbeat to a normal rhythm. For people who have permanent AF, treatment can successfully control symptoms and prevent complications. Treatment consists primarily of different kinds of medicines or nonsurgical procedures.

Antiarrhythmic drug (AAD) therapy has been the current standard first-line treatment, however, AAD therapy is ineffective at controlling AF in approximately half of patients treated with drug therapy.[iv]

Who has atrial fibrillation?

Comparing 2017 to 1998 standardized AF incidence increased by 30% (322 vs. 247 per 100 000 person-years; adjusted incidence ratio [IRR] 1·30, 95% CI 1·27–1·33). Absolute number of incident AF increased by 72% (202 333 vs. 117 880), due to an increasing number of older persons.[v]

The race for pulsed field ablation market share is intense

Treating AF with ablation (electrophysiology/EP) is an $8 billion market with a long runway, according to Travis Steed, a medtech analyst at Bank of America. Steed estimates that only about 15% of the eligible 2.5 million U.S. patients with AF are currently being treated with ablation (worldwide, around 650,000 ablations versus 35 million patients with AF, he notes).

Pulsed Field ablation and Electroporation

Electrophysiologists[vi] are excited. They can hardly contain themselves!

Electrophysiologist

An electrophysiologist is a doctor who’s an expert in diagnosing and treating issues with your heart’s electrical system. A type of cardiologist, they can do testing to find which area in your heart is causing a problem with your heart rhythm. Then they can fix the issue, sometimes right after the diagnostic procedure.

 

This type of ablation is new and improved. Previously, tissue was ablated by burning (radiofrequency) or freezing (cryo).[vii] The esophagus, phrenic nerve, pulmonary veins are very resistant to the pulsed electric field energy source, so collateral damage is nonexistent or minimized.

A total of 383 patients were enrolled between March 2021 and November 2021; 300 were included in the primary analysis cohort, with an average of 5.8 patients treated per operator. In total, 146 of 150 (97%) patients with paroxysmal AF and 141 of 150 (94%) patients with persistent AF completed follow-up.

Treatment success occurred in 100 patients in the paroxysmal AF cohort and 83 patients in the persistent AF cohort (1-year Kaplan-Meier estimates, 66.2% [95% CI, 57.9 to 73.2] and 55.1% [95% CI, 46.7 to 62.7], respectively.[viii]

Postablation voltage map of left atrium. The map demonstrates acute pulmonary vein isolation. Gray areas represent ablated or electrically isolated tissue around the 4 pulmonary veins.

Freedom from atrial arrhythmia recurrence at 12 months was 70% in the paroxysmal cohort and 62% in the persistent. Additionally, clinical success, freedom from recurrence of any symptomatic atrial arrhythmias, was 80% for paroxysmal and 81% for the persistent cohort.[ix]

This is the Medtronic Effort.
Boston Scientific is also in the game, and may have better results. Their entry is called Farapulse.

In Europe, the wait list in the Netherlands for Farapulse is 4 months. They perform 800 procedures per year. Currently they are doing 5-6 patients per day. On average, a case lasts about an hour. Sometimes one is done in 35 minutes. It is a same day discharge.

  • Results demonstrated superiority of the FARAPULSE PFA System in the study's secondary safety endpoint with significantly less post-ablation narrowing of the pulmonary veins at three months (0.9%) compared to the thermal ablation arm (12%).[x]

Europe has been doing Farapulse for 2 years. The Farapulse device received CE mark in 2021 and has been used to treat more than 25,000 patients globally to date. Not yet available in the United States. FDA approval for Farapulse is anticipated in 2024.


[iv] Wazni OM, Dandamudi G, Sood N, et al. Cryoballoon Ablation as Initial Therapy for Atrial Fibrillation. N Engl J Med. January 28, 2021;384(4):316-324.